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Significant Accounting Policies - Additional Information (Details) | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Jan. 01, 2019 USD ($) | Sep. 01, 2018 USD ($) | Jul. 01, 2017 USD ($) | Jul. 01, 2015 agreement
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Date of discontinued recognition of interest on mortgage and commercial loans | 90 days |  |  |  |  |  |
Consumer and other retail loan due date | 120 days |  |  |  |  |  |
Minimum duration for past due residential loans to be considered as nonperforming | 90 days |  |  |  |  |  |
Payments made to FDIC to terminate loss share agreements | $ 0 | $ 0 | $ 4,849,000 |  |  |  |
Impairment of company's goodwill | $ 0 | $ 0 | $ 0 |  |  |  |
Lock in period for interest rates | 45 days |  |  |  |  |  |
Subsequent Event | Accounting Standards Update 2016-02 |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Operating Lease, Right-of-Use Asset |  |  |  | $ 55,000,000 |  |  |
Operating Lease, Liability |  |  |  | $ 55,000,000 |  |  |
Premises |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Estimated life (in years) | 40 years |  |  |  |  |  |
Furniture and equipment |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Estimated life (in years) | 7 years |  |  |  |  |  |
Computer equipment | Minimum |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Estimated life (in years) | 3 years |  |  |  |  |  |
Computer equipment | Maximum |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Estimated life (in years) | 5 years |  |  |  |  |  |
Heritage Financial Group |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Number of loss sharing agreements acquired | agreement |  |  |  |  |  |  | 2
Brand Group Holdings, Inc. |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Cash surrender value of life insurance |  |  |  |  | $ 40,081,000 |  |
Metropolitan Bancgroup, Inc. |  |  |  |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |  |  |  |
Cash surrender value of life insurance |  |  |  |  |  | $ 19,283,000 |

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